U.S. Pat. No. 5,007,480 discloses drilling mud and oil well cement slurries for different purposes such as well cementing, completion fluids, packer fluids, drilling fluids, isolation fluids and other related fluids containing manganomanganic oxide particles as a weight agent. The particle size of the manganomanganic oxide particles is generally below 10 microns with an average particle diameter less than 1 micron.
One drawback with the use of the manganomanganic oxide particles disclosed U.S. Pat. No. 5,007,480 is the poor flow characteristics of the dry particles. Both for offshore and on-shore use of the manganomanganic oxide particles, it would be convenient to use silos for handling and storing the material. However, due to the poor flow characteristics of the material, it is difficult to discharge the material from silo-trucks, silos of delivery boats or stationary silos because the fine particles tend to form bridges in silos and handling systems, particularly in the presence of moisture.
For the same reasons, clearly, metering and feeding of the material into drilling mud and oil well cement slurries from a silo of any size by the use of screw conveyors or vibrating devices is inaccurate and unreliable, or sometimes even impossible.
The manganomanganic oxide particles lose their flowability after handling and may no longer flow freely after being stored at a site, even for a short time. This may require substantial human effort to remove material from a blocked silo, unless the silo is specially designed and fully equipped with special and expensive devices to handle sticky materials. In some instances, the material may therefore also be difficult to move over longer distances using pneumatic transport systems, as are commonly used in the industry.
Material handled in big bags shows a similar lack of flowability, and emptying a big bag through a bottom spout might become impossible with the result that the whole bottom of the bag might need to be cut away to get the material out.
In order to solve flowing and dusting problems of the manganomanganic particles, it is proposed in EP 1776435 B1 to make spray dried granules by first making a liquid slurry (containing 5-35% by weight of manganomanganic oxide, water and at least one water-reducing agent, and/or at least one binder agent and/or at least one dispersing agent) and spray drying the slurry to provide granules. The granules can then later be re-dispersed in water or oil when used for drilling muds or oil well cement slurries. The method of EP 1776435 does however have the disadvantages that the spray drying process requires a significant amount of energy, and that it sometimes can be difficult to re-disperse the granules fully into individual particles.
The manganomanganic oxide particles comprise at least 90% by weight of manganomanganic oxide (Mn3O4), the reminder being calcium oxide, magnesium oxide and preferably less than 1% by weight of elemental manganese. The density of the manganomanganic oxide particles is between 4.7 and 4.9 g/cm3 and they have a particle size of at least 98% below 10 μm.